The investigators propose to compare the "potential beneficial effects" of two contraceptive pills in the prevention of lactation-induced demineralization. A randomized study is proposed to compare Loestrin(an estrogen-containing agent) with Micronov(a progesterone agent). Contraceptives will be administered in the normal dose from 4 weeks to 6 months post-delivery. Bone mineralizaation will be assessed by DEXA at the onset of contraception therapy and at 6 months post-delivery.